Anti-heave protective system

ABSTRACT

Anti-heave protective system comprising a bulky wall structure having a closed contour, and a plurality of vertically spaced energy dissipating beams supported by a plurality of posts arranged in closed contour around the wall structure, at a distance sufficient to dip into the water mass moving up and down in front of the wall structure, to slow down and phase-shift the water motions relative to the heave.

United States Patent [191 Lamy [ Nov. 25, 1975 ANTl-HEAVE PROTECTIVESYSTEM [75] lnventor: Jacques Edouard Lamy.

Fontenay-aux-Roses, France [30] Foreign Application Priority Data Jan.18, 1972 France n 72.01560 [52] U.S.Cl. 6l/3;6l/4;6l/46 [51] Int. Cl.E02b 3/06 [58] Field of Search 61/3, 4. 5.1.46, 49

[56] References Cited UNlTED STATES PATENTS 1.353.001 9/1920 Uriarte 1.6l/4 2.612.758 10/1952 Wets et al... 61/4 3,ll8,282 H1964 .larlarl i l 1t 61/4 3,552,131 l/l97l Mottetali t 4 i 61/46 Primary Examiner-JacobShapiro Attorney. Agent, or Firm-William J Daniel [57] ABSTRACTAnti-heave protective system comprising a bulky wall structure having aclosed contour. and a plurality of vertically spaced energy dissipatingbeams supported by a plurality of posts arranged in closed contouraround the wall structure. at a distance sufficient to dip into thewater mass moving up and down in front of the wall structure. to slowdown and phase-shift the water motions relative to the heave.

12 Claims. 23 Drawing Figures U.S. Patent N0v.25, 1975 Sheet10f63,921,408

U.S. Patent Nov. 25, 1975 Sheet20f6 3,921,408

US. Patent Nov. 25, 1975 Sheet 3 of6 3,921,408

U.S. Patent Nov. 25, 1975 Sheet40f6 3,921,408

US. Patent N0v.25, 1975 Sheet50f6 3,921,408

US. Patent Nov. 25, 1975 Sheet6 0f6 3,921,408

H0122 FIG. .23

ANTI-HEAVE PROTECTIVE SYSTEM This is a continuation-in-part of myco-pending US. patent application Ser. No. 324,305 filed Jan. I7, 1973The invention covers protective systems against wave and heave effectsand especially applies to the protection of port facilities and offshorefacilities.

The development of problems raised by such facilities, especiallyrelated to the development of oil industry and the exploitation ofsub-marine deposite, created an increased need for adequate systemswhich can protect marine facilities against heave and wave effects. Inthe existing systems, one mainly attempts to dissipate wave and heaveenergy, for instance between the blocks of rough stones in aconventional breakwater or through the apertures of a perforated caissonbreakwater. This invention permits an efficient protection to beachieved using various means which can be used in combination with abreakwater of a known type in order to improve the protection providedby the latter.

It is well known an important effect of an obstacle opposed to heave(for instance a vertical wall opposed to a heave normally oriented toits plane) is the heave reflection on the obstacle against the incidentheave. It results in an amplification of the incident heave amplitude onthe obstacle, the latter creating a force field which increases theincident energy. A protective system against heave effects will thenhave to reduce the reflection of the incident heave.

The invention is based on the remark that the reflection occurs whilethe fluid which has been projected upwards at the time of a surge impactis falling down, and the invention consists in slowing down the energyrestitution to the heave by dissipating the energy of the fluid while itis raising up, then falling down in front of the obstacle. The raisingand falling fluid energy along the obstacle is therefore partiallyabsorbed and phaseshifted with respect to the incident heave.

To do this, according to the invention, ascending and descending motionsof the fluid are opposed to by energy dissipating members arranged infront of the bstacle so as to dip into the water mass under motionbeyond the boundary layer thereof.

The energy dissipating members can be material elements resting over thesurface of the obstacle or arranged against this surface and projectingin front of the obstacle. They must slow down the projection of a watermass well above the incident heave peak level, then slow down water fallalong the obstacle. The geometric shapes of the material elements whichcan be obtained in sculpturing them out of the obstacle or in securingon its surface separated elements, shall be selected so that theseelements will rather deeply penetrate beyond the boundary layer to thewater moving up and down along the obstacle to efficiently reduce itsenergy. The sculptures and all other material elements should not createstill water zones covered by a boundary layer beyond which the runningfluid is moving without encountering any obstacle. This is a problemwell known in thermal exchanges between a fluid and a thermal wall, thesolutions of which can be used, save on the scale, to solve the abovementioned difficulty. The material elements of the invention maycomprise separated and discontinuous elements which constitutestructures permitting water drainage, and which can be made under theform of discontinuous inclined slots, studs or bars projecting from theobstacle surface and arranged in staggered relation as eddy generatorsor sending the fluid towards shocks against other elements or againstother portions of fluid, with cancellation of the trend to create alimit layer. 5 In an embodiment, the system of the invention includes awall provided, on its front face exposed to heave action, withprojecting studs arranged in staggered relation and preferably unevenlydistributed. These studs can show, on straight section, asymmetri calprofiles and/or inclined profiles over the general direction of theascending and descending motions of the fluid (i.e. inclined over thevertical line), so as to introduce into these motions a circulationgenerating fluid deviations and end eddies at the stud ends andtherefore an instability of the stud boundary layer likely to preventbuilding up of the boundary layer.

The projecting studs can be easily derived, in con structive manner,from other anti-heave systems. They can consist, for instance, in pipesdraining water through the apertures of a perforated wall of abreakwater of the perforated caisson type.

In another embodiment, studs can be replaced by a system involvinglinear slots and baffles. According to the wall construction mode, itcan be easier to provide discontinuous linear force motion fenderingdevices arranged in such a way that they prevent the wall limit layerfrom being created. For instance, these motion fendering devices can besimilar in shape, save on scale, to heat exchanger blades or centrifugalgimblets.

Also in another embodiment, the protective system of the inventioninvolves a plurality of separate obstacle members arranged in staggeredrelation to provide a substantially uninterrupted impigement area forthe heave, a Colonnade, for instance.

In another embodiment, the obstacle is a bulky wall structure having aclosed contour such as a cylindrical or lobate structure with a verticalcenterline-, and the energy dissipating members comprise a plurality ofbeams supported in vertically spaced relation by a plurality of postsarranged in closed contour around the wall structure. The bulky wallstructure is exposed to the impact of successive surges of the heave toinduce along the wall structure ascending and descending motions of amass of water of a thickness greater than a limit layer of water, andthe beams are supported at a distance from the bulky wall structuresufficient to dip into the mass of water beyond the limit layer, thebeams serving to slow down said ascending and descending motions andphase-shift the same with respect to the heave.

Preferably, the clearance between adjacent beams is at least about Imeter in vertical direction and the width of the beams is in the rangeof about 50 centimeters and about L50 meter in radial direction of thestructure, to produce a significant energy dissipating effect. Stillmore preferably, the vertical clearance is about 2 meters.

The beams preferably have a cross-section which is flattened to be widerthan high, such as a diamond shaped cross-section or a bevelledcross-section.

The following description completed by attached drawings given as nonlimitative examples, will help in explaining how the invention can beachieved.

FIG. 1 is a partial view, in vertical crosssection. of a heaveprotective wall provided with studs;

FIG. 2 is a partial elevation view of the wall shown on FIG. I;

FIG. 3 shows a partial view similar to that shown on FIG. 2. showing amodification:

FIG. 4 shows a perspective view of a stud represented on FIG. 3:

FIG. 5 shows a partial view similar to that on FIG. 1. showing anothermodification;

FIG. 6 is a partial view similar to FIG. 2, showing anothermodification.

FIG. 7 is a vertical cross-section following line VII- VII of FIG. 6;

FIG. 8 shows a partial perspective view of a modification to theembodiment of FIGS. 6 and 7:

FIG. 9 shows a plane view of a protective system including a verticalColonnade;

FIG. I0 shows an elevation view of a modification to the protectivesystem of FIG. 9;

FIG. 11 shows an elevation view of a protective system involvinghorizontal drums;

FIG. 12 shows a vertical crosssection following line XIIXII shown onFIG. 11:

FIG. 13 shows an elevation view of a protective system involvingvertical and horizontal drums;

FIG. I4 is a cross-section following line XIVXIV shown on FIG. 13;

FIG. 15 is a top plan view of a protective system comprising acylindrical wall structure having a vertical centerline and an energydissipating structure involving a plurality of horizontal circular beamssupported in vertically spaced relation around the wall structure;

FIG. 16 is a larger scale cross-section following line XVIXVI shown onFIG. 15;

FIG. 17 is a perspective view of a part of the protective system shownon FIGS. 15 and 16;

FIG. 18 shows a protective system comprising a lobate wall structurehaving a vertical centerline. and an energy dissipating structureinvolving a plurality of horizontal circular beams supported invertically spaced relation around the wall structure. in cross-sectionfollowing line XVIII-XVIII of FIG. 19;

FIG. 19 is a cross-section following line XIX-XIX of FIG. 18;

FIG. 20 is a perspective view of a part of the protective system ofFIGS. I8 and 19, at a larger scale;

FIG. 21 is an enlarged view of a part of FIG. I8, showing amodification;

FIG. 22 is crosssection following line XXII-XXII of FIG. 21;

FIG. 23 is a view similar to FIG. 22, showing a further modification.

FIGS. 1 and 2 show the upper part of a protective wall 1, whose frontsurface la exposed to heave 2 pro vides an impigement area therefor andis provided with a plurality of studs 3 arranged in several horizontalrows 30. 3b, 3c irregularly spaced over a vertical distance. Studs 3 canbe arranged in regular staggered relation. as shown. or each stud can behorizontally shifted with respect to the studs included in all otherrows. More generally. stud arrangement on surface la can be of any othertype (i.e. other than horizontal rows); however. vertical distancesbetween the adjacent studs are preferably irregular. In the embodimentshown. studs 3 are projecting over the same length 1 in front of surface10, but in other embodiments, length I could vary from one stud toanother.

When a wave is such that the heave arrives against solid wall 1, a partof its energy is transformed into an ascending vertical motion alongsurface In. Should the wall be smooth (i.e. should it not include studs3 or 4 equivalent asperitiesl. water would go up. as shown in 5a indotted line. to a considerable height and would then fall down sogenerating (or contributing to generate) the well known reflection orunderset phenomenon which considerably increases the incident heaveenergy and aggressiveness.

Studs 3 have a noticeable length I. as shown on the Figure. so that theyextend beyond the boundary layer of the fluid which is vertically movingalong surface In. In other words. studs are not short asperities. thepurpose of which would only be to slow down a rather thin fluid layermoving against surface In to make it a still water layer in which theywould be fully sunk. but they penetrate into the wave beyond this layer.Studs 3 so generate in water going up following arrows 6 (FIG. 2) eddies6a which reduce its motion. so that the water only reaches a reducedheight as shown on FIG. 1, in 5. Water which goes down then alongsurface In following arrows 7 is falling from a reduced height andtherefore with a smaller energy which is still reduced by eddies 7awhich are created around studs 3.

In the modification shown on FIGS. 3 and 4, studs 8 having asymmetricalprofiles with respect to the general vertical direction of the ascendingand descending fluid flows introduce in a well known manner acirculation of such flows, as shown by ascending current linesschematically drawn in 9. This circulation will increase the energydissipation and result in fluid deviations and eddies at the stud ends(Prandtl end effect). These eddies have been schematically shown in 10on FIG. 4, for the descending flow. the deviations and these eddiescontribute to the instability of the stud limit layer.

On FIG. 5. wall 11 is the front wall. face of which is exposed to heaveeffects, of a perforated caisson which reduces the heave energy, in awell known manner. leaving water flowing through holes 12 between face110 and the caisson included between the other face 11b of the wall andanother wall which is not shown in the Figure. According to aparticularity of the invention, holes 12 are made in wall 11 (which ismade of concrete, for instance) by pipes 13 projecting on face 110 ofthe wall, so constituting studs which absorb a part of the ascending anddescending flow energy, as it is the case in the embodiments shown onthe previous Figures and which modify the flow through holes 12 inattenuating the Honda phenomenon. The ends of pipes 13 can be bevelledas shown in 130, so permitting the hole output to be modified(preferably in increasing their output while ascending water motionstake place, as shown by arrow 14) and eddy generation to be favoured, atpipe ends as shown in 14a.

FIGS 6 and 7 show an embodiment in which studs have been replaced bydiscontinuous linear blade sections 15 projecting on face 16a of wall16. These linear blade sections are inclined laterally and define aplurality of slots 17 therebetween. The inclined and discontinuousarrangement of these blades prevents water from generating still waterzones in slots 17.

When the arrangement of the wall or obstacle on which these blades areresting so permits, blades such as blades 15 are spiral wound, so thatascending and descending flows are subject to a centrifugal effect whichprevents still water zones from being generated in the slots andboundary layer from building up on the blades. For instance on FIG. 8,blades 18 are spiral wound over outside surface 19a of a circular wall19 designed to protect an offshore structure.

In the embodiment shown on FIGS. 1 through 8, the spreading-out surfaceof the system, providing the impigement area for the heave and energydissipating material elements, is a wall face. However, it could be ofadvantage to arrange the material elements on a plurality of separateobstacle members staggered in a direction perpendicular to the systemspreading-out front surface, to provide the substantially uninterruptedimpigement area. For instance one can see on FIG. 9 a colonnade made ofseveral vertical columns 20 arranged in regular staggered relation andprovided each with energy dissipating elements 21 which can be studs orany other type of elements as described on the previous Figures. Alarger and efficient wet surface is then obtained.

In other embodiments, the obstacle means involves one or severalColonnade areas and one or several solid areas. On FIG. for instance,this is a wall which alternatively includes solid horizontal strips 22and horizontal strips 23 made of colonnades similar to those shown onFIG. 9. This arrangement permits a cheaper cost and reduces thedifficulty likely to be encountered when constructing the obstacle meansin placing the most efficient part thereof approximately at the mediumwater level in calm weather, the said most efficient part extending overthe tide range with an appropriate margin for heave amplitude. It goeswithout saying that the columns can be of any section, polygonal withrectilinear sides, convex or concave for instance, and that a more orless strict alternation can be provided between solid portions andcolonnades.

The Colonnade shown on FIG. 9 or the Colonnade areas such as those shownon FIG. 10 can be replaced by several horizontal drums 24 arranged inregular staggered relation (FIGS. 11 and 12) or by horizontal drums 25crossed with vertical drums 26 (see FIGS. 13 and 14).

The protection constituted by colonnades, horizontal or crossed drums,or by their alternation with solid zones will follow the contour of thestructure to be protectecl, at a convenient distance from the latter.This structure could be a beach, a wharf or a tank which will beenclosed by the protective system. The distance between the structureand the system will be defined taking into account the residual heavereflected by the structure, on which the protective system operates fromits rear face to reduce it. This distance can be small.

When the structure to be protected (wharf or tank, for instance)includes a vertical or almost vertical wall, it can constitute with theprotective colonnades installed behind it a kind of caisson acting as aperforated caisson in order to contrib ute to the heave energydissipation.

It should be noter that in a protective system made of concrete,including solid portions alternating with colonnades or horizontal orcrossed drums zones, the columns or drums can be used to pass prestresssteel reinforcing elements ensuring the strength of the structure andcolumns proper (or drums). These steel reinforcing elements can becables passing through pipes which are then filled of concrete to obtainthe columns or drums. This remark especially shows that in addition totheir heave reducing effect, horizontal drums can also play a veryuseful part in the structure strength.

FIG. shows a circular wall 27 designed to protect an offshore structure(not shown on the Figure). At a distance around wall 27, a plurality ofposts or columns 6 28 have been arranged in a circle to support aplurality of horizontal circular beams or string-courses 29 forming withthe columns a kind of grid, as shown on FIG. 17. The edifice includingwall 27 and grid 28, 29 is completed by a plurality of braces 30connecting the wall and the grid. The edifice is made of reinforcedconcrete and, to facilitate building operations, columns 28,string-courses 29 and braces 30 are rectangular in section. Grid 28, 29is capped by an upper circular beam or roofing 31 which is alsorectangular in section. Prestress steel reinforcing units 32 passthrough the columns, beams and braces.

AS the waves impinge against circular wall 27, they will induceascending and descending motions of a mass of water which will in turnwash a number of the horizontal circular beams 29, 31 and the latterwill generate energy dissipating eddies like the material elements ofthe embodiments already described.

It will be appreciated that, in FIGS. 15 to 17, the circular beams aresupported cantilever in front of the posts, so that the fullcross-sections of the beams project radially outwardly of the posts.This construction makes it possible to obtain a good energy dissipatingeffect with a short spacing of the posts, because the full lengths ofthe beams are useful for this purpose.

FIGS. l8-20 show an energy dissipating structure of easier construction,in which the radially outer and inner surfaces 33a, 33b of horizontalcircular beams 33 are flush with the radially outer and inner surfaces34a, 34b of posts 34, respectively. This construction mode does notreduce significantly the energy dissipating effect of the beams, becausethe spacing of the posts is much greater than in FIGS. 15-17, and thebeams can work along substantial lengths between the posts.

Moreover, the bulky impigement structure of FIG. 18 comprises a lobatewall structure 35, that is to say a wall made of a plurality ofpart-cylinder portions 35a, 35b, 35c, 35d, 35e. 35f having verticalcenterlines to form a festooned cross-section as shown. The posts areconnected to the wall structure by a plurality of pairs of braces 36, 37joining at the intersections 38 of the lobes.

Wall 35 is designed for supporting a double decked platform 38 above thesurface of the sea 40, to receive offshore industrial plants such as anoil winning or processing plant. Wall 35 and posts 34 are built upon acommon foundation raft 41 which is made to rest on the bottom of the sea42.

Here again, wall structure 35, beams 33, posts 34 and braces 36, 37 aremade of reinforced concrete, and are used for the passage therethroughof prestress steel units 32.

As already stated, the horizontal beams should have a substantial widthin radial direction and should be substantially spaced in verticaldirection, in order to dissipate energy of the waves to a considerableextent. For example. in an embodiment of FIGS. 15-17, beams 29 are onemeter wide and the vertical clearance between adjacent beams in 1 meteras well. In an embodiment of FIGS. l820, beams 33 are 1 meter wide andthe vertical spacing is 2 meters.

The height of the energy dissipating beams is immaterial, and the beamspreferably have a cross-section which is flattened to be wider thanhigh. In other words, the horizontal beams may be given a height lessthan their radial width, in order to reduce the horizontal thrust orpressure applied thereto by the waves. Also, the posts may be flattenedor streamlined in cross-section, ie have a relatively thinner widthcircumferentially to the energy dissipating structure than radiallythereto. in order to reduce the horizontal thrust or pressure of thewaves. FIGS. 21-23 show embodiments in which both the beams and postshave such flattened corss-section. ln FIGS. 2] and 22 both beams 43 andposts 44 have diamond shaped cross-sections. In FIG. 23, beams 45 havebevelled cross-sections.

I claim:

1. Protective system against the heaving action of waves of watercomprising a bulky obstacle means having a spreading-out surface andproviding a substantially uninterrupted impingement area of substantialextent athwart the wave path and exposed to the impact of successivesurges of the heave to induce along said spreading-out surface alternateascending and descending motions of a mass of water of a thicknessgreater than a boundary layer of water. and means providing a pluralityof energy dissipating material elements in front of said spreading-outsurface at a distance sufficient to penetrate into said mass of waterbeyond said boundary layer, said elements serving to slow down ascendingand descending water motions and phaseshift the same with respect to theheave. said bulky obstacle means comprising a bulky wall structurehaving a closed contour and exposed to the impact of said successivesurges of the heave. and said energy dissipating material elementscomprising an energy dissipating structure arranged in closed contouraround the bulky wall structure and comprising a plurality of beams anda plurality of posts supporting the beams in vertically spaced relationat a distance from the bulky wall structure sufficient to dip into saidmass of water beyond said boundary layer.

2. Protective system as claimed in claim 1, in which the bulky wallstructure comprises a cylindrical wall having a vertical centerline.

3. Protective system as claimed in claim 1, in which the bulky wallstructure comprises a lobate wall having a vertical centerline.

4. Protective system as claimed in claim 1, in which the beams projectradially outwardly of the posts.

5. Protective system as claimed in claim 1, in which the beams haveradially outer surfaces which are substantially flush with radiallyouter surfaces of the posts.

6. Protective system as claimed in claim 1, in which the beams aresupported with at least about 1 meter clearance between adjacent beams,in vertical direction.

7. Protective system as claimed in claim 6, in which the clearance isabout 2 meters.

8. Protective system as claimed in claim I, in which the beams have awidth in the range of between about 0.50 meter and about [.50 meter inradial direction of the energy dissipating structure.

9. Protective system as claimed in claim 8, in which the beams have aheight less than said width.

10. Protective system as claimed in claim 9, in which the beams havediamond shaped cross-sections.

11. Protective system as claimed in claim 9, in which the beams havebevelled cross-sections.

12. Protective system against the heaving action of waves of watercomprising a bulky obstacle means having structure spreadingout surfaceand providing a substantially uninterrupted impingement area ofsubstantial extent athwart the wave path and exposed to the impact ofsuccessive surges of the heave to induce along said spreading-outsurface alternate ascending and descending motions of a mass of water ofa thickness greater than a boundary layer of water, and means providinga plurality of energy dissipating material elements in front of said spreadingout surface at a distance sufficient to penetrate into said massof water beyond said boundary layer, said elements serving to slow downascending and descending water motions and phaseshift the same withrespect to the heave, said bulky obstacle means comprising a reinforcedconcrete wall structure having a closed contour and exposed to theimpact of said successive surges of the heave, and said energydissipating material elements comprising an energy dissipating structurearranged in closed contour around the wall structure and comprising aplurality of reinforced concrete beams, and a plurality of reinforcedconcrete posts supporting the beams in vertically spaced relation at adistance from the bulky wall structure sufficient to dip into said massof water beyond said boundary layer, at least one platform supported bythe wall structure above the water level, a plurality of reinforcedconcrete radiant braces connecting the energy dissipating structure tothe wall structure; and prestress steel units passing through the wallstrcture and through the beams, posts and braces. =l

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,921,408 Dated November 25 1975 1nventor(s) Jacques Edouard Lamy It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Item 73, should read C. G. Doris (Compagnie Generale pour lesDeveloppements Operationnels des Richesses Sous-marines) Paris, FranceSigned and Sealed this twenty-seventh D3) of ApriI1976 [SEAL] Attesr:

RUTH C. MASON C. MARSHALL DANN Alltsiing ()jfizer Commissioner 0]lalenrs and Trademarks

1. Protective system against the heaving action of waves of watercomprising a bulky obstacle means having a spreading-out surface andproviding a substantially uninterrupted impingement area of substantialextent athwart the wave path and exposed to the impact of successivesurges of the heave to induce along said spreading-out surface alternateascending and descending motions of a mass of water of a thicknessgreater than a boundary layer of water, and means providing a pluralityof energy dissipating material elements in front of said spreading-outsurface at a distance sufficient to penetrate into said mass of waterbeyond said boundary layer, said elements serving to slow down ascendingand descending water motions and phaseshift the same with respect to theheave, said bulky obstacle means comprising a bulky wall structurehaving a closed contour and exposed to the impact of said successivesurges of the heave, and said energy dissipating material elementscomprising an energy dissipating structure arranged in closed contouraround the bulky wall structure and comprising a plurality of beams anda plurality of posts supporting the beams in vertically spaced relationat a distance from the bulky wall structure sufficient to dip into saidmass of water beyond said boundary layer.
 2. Protective system asclaimed in claim 1, in which the bulky wall structure comprises acylindrical wall having a vertical centerline.
 3. Protective system asclaimed in claim 1, in which tHe bulky wall structure comprises a lobatewall having a vertical centerline.
 4. Protective system as claimed inclaim 1, in which the beams project radially outwardly of the posts. 5.Protective system as claimed in claim 1, in which the beams haveradially outer surfaces which are substantially flush with radiallyouter surfaces of the posts.
 6. Protective system as claimed in claim 1,in which the beams are supported with at least about 1 meter clearancebetween adjacent beams, in vertical direction.
 7. Protective system asclaimed in claim 6, in which the clearance is about 2 meters. 8.Protective system as claimed in claim 1, in which the beams have a widthin the range of between about 0.50 meter and about 1.50 meter in radialdirection of the energy dissipating structure.
 9. Protective system asclaimed in claim 8, in which the beams have a height less than saidwidth.
 10. Protective system as claimed in claim 9, in which the beamshave diamond shaped cross-sections.
 11. Protective system as claimed inclaim 9, in which the beams have bevelled cross-sections.
 12. Protectivesystem against the heaving action of waves of water comprising a bulkyobstacle means having structure spreadingout surface and providing asubstantially uninterrupted impingement area of substantial extentathwart the wave path and exposed to the impact of successive surges ofthe heave to induce along said spreading-out surface alternate ascendingand descending motions of a mass of water of a thickness greater than aboundary layer of water, and means providing a plurality of energydissipating material elements in front of said spreadingout surface at adistance sufficient to penetrate into said mass of water beyond saidboundary layer, said elements serving to slow down ascending anddescending water motions and phaseshift the same with respect to theheave, said bulky obstacle means comprising a reinforced concrete wallstructure having a closed contour and exposed to the impact of saidsuccessive surges of the heave, and said energy dissipating materialelements comprising an energy dissipating structure arranged in closedcontour around the wall structure and comprising a plurality ofreinforced concrete beams, and a plurality of reinforced concrete postssupporting the beams in vertically spaced relation at a distance fromthe bulky wall structure sufficient to dip into said mass of waterbeyond said boundary layer, at least one platform supported by the wallstructure above the water level, a plurality of reinforced concreteradiant braces connecting the energy dissipating structure to the wallstructure; and prestress steel units passing through the wall strctureand through the beams, posts and braces.